DES MOINES — President Obama struck back Thursday against criticism from rival Mitt Romney over the spiraling national debt, arguing that his administration has allowed federal spending to grow at the slowest rate in six decades and charging that Romney’s tax policies would run up the tab far faster.

Appearing at a campaign rally at the Iowa State Fairgrounds, Obama offered a firm rebuttal to Romney’s contention, made during a speech in this city two weeks ago, that the president had overseen a “prairie fire of debt.”

Rather, Obama argued, it was Republicans who ran up the tab through two wars and a series of tax cuts and stuck his administration with the bill.

“We’re sitting there at the restaurant wondering what do with all the steaks and martinis,” Obama told a crowd of more than 2,000 at an exhibition hall decked out with two huge American flags and the campaign slogan “Forward” on a giant poster.

Romney’s speech was a “cow pie of distortions,” Obama said. What Romney did not mention, he added, was that the presumptive GOP presidential nominee wants to enact a tax cut for wealthy Americans that would only add to the debt.

“That is like trying to put out a prairie fire with some gasoline,” Obama said. “I refuse to let that happen to our country.”

The impassioned address, which drew enthusiastic shouts and chants, came at the end of a two-day road trip during which Obama continued his assault on Romney’s record as the former head of Bain Capital, a private-equity firm. During several fundraisers in Colorado and California, Obama argued that while Romney is a patriotic American who should be proud of his private-sector success, he has learned the wrong lessons about the economy to become president.

The strategy made clear that the Obama campaign intends to continue to make Romney’s time at Bain a central campaign issue, despite misgivings among Republicans and some Democrats who have criticized the president for attacking private equity as an American institution.

Even Obama’s decision to appear at the fairgrounds was calculated to inflict maximum damage on Romney, who suffered one of his most ignominious moments here last summer when he said that “corporations are people” during a contentious exchange with Iowans at a state fair.

That comment has haunted the former Massachusetts governor as he attempts to sell his own economic message to independent voters. On Thursday, the Obama campaign distributed a new video clip featuring Romney’s Iowa appearance last summer, and the president pointedly repeated Romney’s line during his own speech, drawing boos from the crowd.

For his part, Romney has touted his business success as helping to prepare him to improve the U.S. economy, and he attacked the president for failing to speed up economic growth. The national debt stands at $15.7 trillion. During a visit to Des Moines two weeks ago, Romney described Obama as a reckless spender whose policies have contributed to “a prairie fire of debt sweeping across Iowa and our nation.”

“Every day we fail to act, that fire gets closer to the homes and children we love,” Romney said.

Before appearing in Des Moines, Obama visited Newton, where he called on Republican rivals to support new tax credits for companies that produce wind power.

Obama used an appearance at TPI Composites, which makes blades for wind turbines, to emphasize his campaign message that his administration is focused on economic growth that promotes a strong, enduring middle class.

After touring the company, Obama told a crowd of supporters on the factory floor that the tax credits first enacted in 2009 as part of his economic stimulus are set to expire if Congress does not pass an extension by year’s end. Without the tax break, as many as 37,000 jobs could be lost, according to administration officials and industry experts.

“If Congress doesn’t act, companies like this one will take a hit,” Obama said. “Jobs will be lost. That’s not a guess. That’s a fact. We can’t let that happen.”

Obama assailed congressional Republicans with many of the same themes he has used on Romney. The extension of the proposed wind power tax cut is among five economic initiatives on the “to-do list” that Obama has challenged Republican lawmakers to support in an increasingly partisan election year.

“Our dear friends in Congress are standing in the way,” the president said. “They either want to do nothing at all, or they want to double down on the same failed policies.”

White House officials said they are hopeful that Congress will support the wind-power tax credit, which has bipartisan support. In March, Sen. Charles E. Grassley (R-Iowa) was among a group of senators who called for a two-year extension of the credit.

But in a statement Wednesday, Grassley criticized Obama for stumping for the plan in the senator’s home state rather than directly discussing it with congressional leaders. “The president could exert his leadership by working with Congress on a way forward instead of calling for a provision that’s a no-brainer for many of us,” Grassley said. “He’s focusing on the easy part of a bigger task. The stakes for the wind industry and the country in general will only get worse with delay. It’s time to act, not politick.”

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